Free delivery controlled return valve



Patented Mar. 18, 1969 3,433,253 FREE DELIVERY CONTROLLED RETURN VALVE Lewis P. T omer, Mentor, Ohio, assignor to Fluid Controls, Inc., Mentor, Ohio, a corporation of Ohio Filed Apr. 14, 1967, Ser. No. 631,042 US. Cl. 137--493 9 Claims Int. Cl. F16k 17/26 ABSTRACT OF THE DISCLOSURE The present disclosure is directed primarily to a bydirectional control valve for a hydraulic hoist. The structure permits relatively free flow through the body from the inlet to the outlet, but restricts the flow from the outlet to the inlet in response to the pressure of fluid at the oulet side as modified by the action of a time delay means.

This invention relates to a free delivery controlled re turn valve particularly useful in hydraulic hoist circuits. The present valve permits relatively free flow of hydraulic fluid from a pump to a hoist cylinder for hoisting a load and, during the hoisting operation, is automatically set by the pressure exerted by the hydraulic fluid being delivered to the hoist by the pump into lowering positions such that during lowering of the load, the return flow is reduced to a rate so proportioned to the weight of the load being lowered, that the load is lowered at a safe speed.

The co-pending application of Robert F. De Marco, Ser. No. 448,919, filed Apr. 19, 1965, entitled, Load Lowering Valve for Hydraulic Hoists, and assigned to the same assignee, discloses a valve for the same purposes, but which, should it fail in operation necessarily would not fail safe, but could permit lowering of the load at dangerous speeds.

In a later co-pending application of the said Robert F. De Marco, about to be filed and executed, Ser. No. 619,- 372, filed Feb. 28, 1967, and entitled Free Delivery and Variably Restricted Return Valve, and assigned to the same assignee, an improved form of the valve of the earlier application is disclosed The improved form is such that should it fail is would fail safe. Theimproved form, however, has a disadvantage in that it responds to the pressure fluid at about the same rate for setting the valve to increase and decrease the rate of return flow, whereas it is desirable that the valve respond more rapidly for reducing the rate of return flow than for increasing such rate. Rapid operation for reducing return flow and slower operation for increasing return flow are desirable. One reason is that a load being hoisted acquires a certain momentum. If the hoisting is suddenly stopped, and the hoist almost instantly operated for lowering, then, even though the valve had been adjusting during hoisting for the proper slower rate of return flow, the dynamic inertial forces urge the load to continue to rise slightly for an instant after the hoisting is stopped, thus reducing the effective weight of the load on the hoist for an instant. This reduction in effective weight reduces the pressure of the fluid effective at the return side of the valve. Since the valve responds almost instantly and before the inertial flow of the delivery fluid ceases while the effective weight of the load is reduced, the valve readjusts for a lowering rate greater than is safe for actual weight of the load.

When these inertial forces cease, the valve remains so adjusted, and consequently permits too rapid lowering for the actual aoad.

The effects of these inertial forces on the adjustment of the valve for return flow exist only for an instant, after which the load becomes static. Consequently, if the operator, after hoisting, hesitates for an instant before lowering, the pressure on the return side of the valve again increases and reflects the actual weight of the load, and quite often, in this interval, the valve agan adjusts before it seats, for the proper rate of return flow based on actual weight.

Damping means are provided in the improved valve of the later co-pending application for reducing the rate at which the valve increases the rate of return flow, but the same means tend to reduce also the rate at which the valve reduces the rate of return flow.

The valve of the present invention is an improvement on the valve in the later co-pending application in that it retains the fail safe features, yet responds rapidly to the fluid pressure during hoisting for reducing the rate for lowering, and responds much less rapidly for increasing the rate of lowering. As a result, the response to the inertial forces above described is negligible, so that, should the operator shift to lowering before the inertial hoisting forces are dissipated, the setting of the valve for the lowering of the actual weight of the load will be retained.

Other specific structure and advantages of the present invention will become apparent from the following description wherein reference is made to the drawings in which:

FIG. 1 is a top plan view of a valve embodying the principles of the present invention;

FIG. 2 is a right end elevation of the valve illustrated in FIG. 1, showing diagrammatically its connection to a hydraulic circuit of a lift truck;

FIG. 3 is a horizontal fragmentary sectional view of the valve taken on the line 3-3 in FIG. 1;

FIG. 4 is a vertical sectional view of the valve taken on the line 4-4 in FIG. 3; and

FIG. 5 is an enlarged fragmentary, vertical sectional view through the valve and is taken on the line 5--5 in FIG. 4.

Referring to the drawings, the valve comprises a body 1 having an inlet 2 and an outlet 3. As best illustrated in FIG. 2, the inlet 2 is connected to a motor driven pump 4 and the oulet 3 is connected to a hoist cylinder 5. A piston 6 is reciprocable in the cylinder and is operative upon extension to lift a load L. The body has a valve cavity 10 which is in communication with the inlet 2 and outlet 3. Within the cavity 10 is a valve seat 11 having an orifice 11a. Settable throttling valve means control the effective size of the orifice in an inverse relation to the weight of the load being hoisted. This means includes a check valve plug 12 mounted in the cavity at the discharge side of the seat 11 for rocking movement generally endwise of the axis of the orifice 11a in a direction away from the seat 11 and toward the outlet so as to permit a relatively free flow of pressure fluid from the inlet 2, through the cavity 10 to the outlet 3. The plug is rockable in the opposite direction so as to seat on the seat 11 and restrict the return flow of the fluid. For controlling the degree of restriction of the orifice 11a by the plug 12, the plug is mounted for movement also in opposite directions transversely of the axis of the orifice 11a. To provide for setting the valve, the plug '12 is mounted on a support which preferably is in the form of a piston 14. The piston 14 is mounted in the body for rocking-about its longitudinal axis, which is offset from, and disposed in a plane normal to, the axis of the orifice 11a. The rocking motion is preferably provided by permitting the piston itself to rock about its own longtudinal axis and the transverse movement is effected by the axial movement of the piston.

The valve plug 12 has a notch 15 opening through one of its margins and positioned to be aligned in different degrees with the orifice 11a for controlling the return flow through the valve when the plug 12 is seated in different set control positions to which it has been moved by the piston in a direction transversely of the axis of the orifice.

The valve plug 12 is moved transversely the axis of the orifice while it is held unseated by fluid pressure flowing from the inlet toward the outlet so that there is little resistance to its movement to adjusted positions. The plug 12 is mounted on the piston for rocking forwardly and rearwardly of the piston axis which extends transversely of the piston axis by means of a pivot 16. At the end of the plug 12 opposite from the pivot 16, the plug 12 is provided with a notch 17 which engages a suitable pin 18 which is secured in the valve body and is parallel to the axis of the orifice 11a. A light seating spring 19 is mounted in surrounding relation to the pin 18 and bears against the face of the plug 12 so as to yieldably urge the plug 12 into seating position.

The arrangement of the pivot 16 and pin 18 are such that the movement of the plug 12 in the direction of movement of the piston 14 is not a bodily movement equal to that of the piston. Instead, the plug tends to rock about the pivot 16 and pin 18 when the piston moves axially so that the rate of change in the effective size of the orifice is more readily controlled. In the form illustrated, the movement of the central portion of the plug 12 transversely of the orifice axis is about one half of the piston movement. The rate of change of the effective size of the orifice can be controlled by designing the notch 15 in proper proportions for the results desired.

The piston 14 is provided at one end with an integral rod 21 which extends through a suitable bore 22 in a housing 23. The bore 22 cooperates with the rod 21 to guide the piston. The rod 21 extends through the bore 22 into an enlarged coaxial counterbore 24 in the housing 23. At its other end, the rod 21 carries a cap 25 against which bears one end of a biasing spring 26 which is operative to bias the piston in a direction to cause the valve plug to move transversely of the orifice axis to the least restricting position with respect to the orifice 11a. The end of the counterbore 24 is closed by a suitable plug 27 against which the other end of the spring 26 bears.

The plug 27 has a vent 28 for venting the counterbore to the outside atmosphere so that the end of the rod 21 is not subjected to the pressure of the fluid within the valve cavity 10.

Since the piston rod 21 is not subjected to the pressure of the fluid within the cavity 10, the piston is subjected to a differential in pressure equal to the area of the end of the piston rod 21 times the unit fluid pressure in the cavity 10. This pressure is adequate to drive the piston against the force of the return or biasing spring 26 toward orifice restricting position while the valve plug 12 is being held unseated by the pressure fluid being delivered through the inlet 2 by the pump. Since the head end of the piston 14 is fully exposed to the fluid in the cavity at all times, the response of the piston is almost instantaneous in the direction for reducing the effective orifice area. This is desirable. However, it is desirable also that the return of the plug 12 in the orifice increasing direction be much slower. For this purpose, a cylinder 30 is provided in the valve body in coaxial relation to the piston 14 and a piston 31, having a port 32 therein, is mounted in the cylinder. The piston 31 is urged by a spring 33 in a direction toward the adjacent end of the piston 14 at all times. The piston 14 is provided at the end adjacent the piston 31 with a valve plug portion 35 which is arranged to seat and seal the port 32 when the piston 14 is forced to the left against the piston 31. With this arrangement, when the pressure of fluid in the cavity is sufficient to drive the piston .14 to the right, this movement removes the portion 35 from the port 32 so that fluid flows through the port 32 into the cylinder 30. Under the influence of the spring 33, the piston 31 follows up the piston 14 to the right. Thus, as the plug 12 is moved instantaly to restrict the orifice 11a, the piston 31 is moved instantly in the follow-up relation. If hoisting is stopped and lowering is commenced immediately, the pressure in the cavity 10 is suddenly reduced, due to the inertial forces described, and the spring 26 immediately starts the return of the piston 14 to the left. However, the valve portion 35 of the piston has by this time sealed the orifice 32 so that the piston 14 can move to the left only as fast as it forces the piston 31 to the left. Since fluid is trapped in the cylinder 30 behind the piston 31, the piston 14 can return to the left only as fast as is permitted by leake of the fluid from the cylinder 30 past the piston 31.

By preselecting proper radial clearance of the piston 31 and the wall of the cylinder 30, or otherwise providing a by-pass duct, the desired rate of leakage back into the cavity 10 can be obtained so that the desired damping effect and slower rate of return of the piston 14 and plug 12 can be accurately controlled so as to reduce properly the rate of increasein the effective area of the orifice 11a.

Thus, in operation, the valve plug 12 is readily unseated by the delivered fluid and permits free flow from the inlet 2 to'the outlet 3 to hoist a load. Almost at once upon inition of hoisting of the load and while the plug 12 is unseated, and continuously thereafter during hoisting, the plug 12 is moved to set positions for controlling the lowering of the load. Even though the inertial forces of the load tend to cause it to rise on upwardly and reduce the effective weight of the piston 6, and thereby reduce the fluid pressure in the cavity 10, nonetheless the piston 14 cannot move rapidly to the left as a result of this pressure drop and thus increase the effective size of the orifice 11a. On the contrary, the piston 14 is constrained to slow movement to the left, due to the piston 31. Thus, even without a slight time delay between hoisting and lowering sufficient to permit the inertial forces of the load to dissipate, so that the piston 6 is subjected only to the static load, the valve plug 12 seats in the set orifice restricting position to which it was moved by the piston 14 during hoisting.

As mentioned, the present valve is a fail safe valve, the same as the later of the two above co-pending applications, the principal improvements herein being the damping of the return of the plug 12 in the orifice increasing direction, and the movement of the orifice restricting position of the valve plug 12 in the orifice changing directions by a rocking action of the plug instead of bodily movement of the plug with the piston 14, and the better control obtained thereby.

Having thus described my invention, I claim:

1. A control valve comprising a hollow body having an inlet and an outlet, and a valve cavity therebetween;

settable throttling valve means in the cavity and including a valve seat member having orifice means and a valve plug member movable out of seated position on the seat member to permit a relatively large effective orifice area for flow of pressure fluid from a source through the body from the inlet to the outlet, and movable into seated position to reduce the effective area for flow from the outlet to the inlet, said plug member being settable, while unseated, to set positions wherein, it will, upon reseating, restrict the orifice area in varying degrees depending upon said set positions;

resilient means normally urging the plug member to a set position for maximum effective orifice area for flow of fluid from the outlet to the inlet;

fluid pressure operable means connected to the valve plug member and arranged 'to be subjected to the pressure of fluid in the cavity during changes in said pressure and operable thereby to set the valve plug member, while the plug member is unseated during increases of pressure of the fluid at the outlet side of the seat member, in set positions, for decrescent degrees of effective orifice area for flow from the out let to the inlet, depending upon said increases of pressure;

and means to return the plug member to seated position While it is held by the fluid pressure operable means in the position in which it has been set before the occurrence of substantial flow of pressure fluid from the outlet to the inlet,

characterized in that said fluid pressure operable means comprises a driving member movable substantially instantly in one direction in opposition to the resilient means by the pressure of fluid in the cavity when said pressure exceeds a predetermined pressure,

and time delay means connected to the driving member and operative to delay the return of the driving member by the resilient means when the pressure of the fluid in the cavity drops below a predetermined pressure.

2. The structure according to claim 1 wherein the time delay means includes a cylinder, a damping piston reciprocable therein and urged toward retracted position in the cylinder by said driving member upon return of the driving member by the resilient means, and subject to controlled escape from the cylinder of fluid trapped in the cylinder, so as to delay the return of the piston,

and means operable upon movement of the driving member by the fluid pressure in said one direction to admit fluid readily from the cavity into the cylinder.

3. The structure according to claim 2 wherein the last mentioned means is a check valve operable to admit fluid into the cylinder and obstruct its escape therefrom.

4. The structure according to claim 2 wherein the last mentioned means includes a port in the damping position operable when open to admit fluid readily from the cavity into the cylinder behind the damping piston, a spring which urges the damping piston toward and into contact with the driving member, and said member has valve plug means engageable with the damping piston and restricting said port when the member is returned by the resilient means.

5. The structure according to claim 1 wherein the plug member is supported for rocking movement toward and away from the seat member in a direction generally endwise of the axis of the orifice for seating and unseating, and for movement by the driving member and by the resilient means generally transversely of the axis of the orifice.

6. The structure according to claim 5 wherein the plug member is pivotally supported by a pivot for swinging relative to the driving member generally endwise of the paths of movement of the plug member by the driving member.

7. The structure according to claim 6 wherein means connect the plug member to the body for swinging about the pivot and concurrent floating and pivot movement relative to the body.

8. The structure according to claim 7 wherein the plug member is pivotally connected to the driving member for swinging generally endwise of the path of the driving member, the plug is pivotally connected to the body by a second pivot means for swinging generally endwise of said path relative to the body about the pivot means and for concurrent movement transversely of the pivot means.

9. The structure according to claim 8 wherein the pivot means includes a pivot pin having its axis parallel to said pivot, the plug member has a slot which is of a length in a direction toward the pivot such that the pin can migrate along said slot during the pivotal movement of the plug member about the pivot.

References Cited UNITED STATES PATENTS 1,781,366 11/1930 Campula 137-5133 2,886,065 5/1959 HerShm-an 1-37-513.3 XR 3,298,393 1/1967 Mosier 137-5133 HAROLD W. WEAKLEY, Primary Examiner.

US. Cl. X.-R. 

